DE102008035539B4 - Coupling with a surveying friction plate - Google Patents

Abstract

A clutch (10) comprising: a reaction plate (16) configured to apply a compressive force; a friction plate (12) having a surface opposite the reaction plate; a friction material layer (22) having a first surface attached to the surface of the friction plate (12) and a second surface (24) opposite the reaction plate (16), a plurality of elevations (26 ) of a predefined height relative to the surface (24) of the friction material layer (22), each of which has a cavity (30) of a predefined depth surrounded by an edge (28); and a lubricating fluid (14) disposed between the reaction plate (16) and the friction material layer (22) to transmit the compressive force and to provide a lubrication layer (14) between the reaction plate (16) and the friction plate (12); characterized in that the predefined depth of the cavity (30) is less than the predefined height of the elevations (26), so that lubricating fluid (14) located in the cavity (30) during engagement of the clutch (10) from the cavity (3) is pressed or pressed and flows over the edge (28) onto the surface (24).

Description

TERRITORY

The present invention relates to a coupling with a surveys having friction plate according to the preamble of claim 1, as for example from the US 4,667,534 A has become known.

BACKGROUND

Torque-transmitting devices, such as clutches or brakes, are widely used throughout the automotive industry. For example, automotive transmissions use a plurality of clutches to engage and disengage the gear sets of the transmission to provide forward and reverse gear ratios. The clutch has a reaction plate for applying a compressive force. The clutch further includes a friction plate disposed adjacent to the reaction plate for frictionally engaging the reaction plate to transmit a drive torque between the reaction plate and the friction plate when the compressive force is applied. The clutch further includes a friction material layer adhered to the friction plate and located opposite the reaction plate. The friction material layer is configured to be compressed by the reaction plate. Grooves, slots or recesses may be formed in the friction material layer as in the references US 5,094,331 A . JP 2004 211781 A . EP 0 758 722 A2 . US 2004/0050646 A1 . DE 44 43 096 C1 . DE 15 75 906 B or US 1,833,414 A described couplings is the case.

The clutch further includes a fluid lubricant disposed between the reaction plate and the friction plate to provide a lubricating layer between the plates during engagement of the clutch.

During clutch engagement, there are three predominant lubrication states: hydrodynamic (HD), gentle-elastohydrodynamic (soft-EHD), and boundary state. The hydrodynamic lubrication state is characterized by a thick fluid film thickness, a low nominal contact pressure of the clutch plates, and an extremely low traction / friction coefficient. Thus, torque transfer is difficult to achieve during the hydrodynamic lubrication state.

During the mild elastohydrodynamic lubrication condition, the sharp groove edges and / or the scraper topography of the friction material serve to rupture the hydrodynamic film and create film islands separating the mating surfaces of the clutch plates. The islands are distributed unevenly across the surface due to the nonhomogeneous nature of the friction material, the waviness of the plates, and the uneven load distribution. Since the rated load on the friction plate is constant, the fluid islands experience a much greater pressure than in the hydrodynamic state. As the lubricating fluid becomes thinner, its shear rate rapidly increases, allowing sufficient torque to be transmitted through the fluid.

During the boundary lubrication state, the gentle EHD fluid undergoes decomposition due to a decrease in speed and a temperature rise. Further, the active additives are activated in the surface of the friction material layer and produce a low shear protective fluid layer which acts as a solid lubricant that interacts with the friction material layer to produce a solid to solid coefficient of friction closer to the EHD value is. A tribochemical layer is the result of a chemical reaction between the fluid lubricant additives and the interfaces of the clutch plates. As the fluid lubricant worsens, the tribochemical layer undergoes shearing. The chemical bonds decompose and the additives in the fluid are consumed. The tribochemical layer is replenished using new unused fluid additives. As the additive concentration in the fluid falls below a predefined critical threshold, the local friction coefficient increases in value and results in unequal clutch engagement (shudder or stick-slip) or further temperature increase. Provided that the temperature rises, the high temperature can cause damage to the friction material (wear, cracking and glazing). The reaction plate may also be damaged, which may include heat staining.

The soft-EHD state is the optimum state for the clutch operation for the following reasons: (1) The fluid-thin-film traction provides friction coefficients sufficient to transmit the required torque. (2) The thin film traction does not generate excessive heat, which may damage the friction material (wear, cracking and glazing) and the reaction plate (heat stain), resulting in friction loss and resulting in shudder. (3) The surface-active friction modifiers are not consumed during the soft-EHD state, therefore, the fluid deterioration becomes delayed. As long as the high grade fluid base is selected, the oxidation of much of it is not the primary failure mode of the coupling up to a fluid trough temperature of 135 degrees Celsius. (4) The fluid film as well as the friction material have damping capabilities that reduce the amplitude of self-induced and / or external vibration of the friction interface. (5) The traction / friction coefficient is proportional to the frictional resistance which decreases with increasing temperature (this is typical for the clutch engagement cycle) and positive friction / slip tendency. (6) Compared with other lubrication systems, the clutch can operate in the soft-EHD mode for sufficiently long periods of time without any damage to the interface or its failure.

The invention is therefore based on the object to provide a new and improved coupling that extends the soft-EHD state during engagement of the clutch. The new and improved clutch should maintain a sufficient coefficient of friction and not generate excessive heat damaging the friction material layer of the clutch.

SUMMARY

The present invention therefore provides a coupling having the features of claim 1.

The invention extends the soft-EHD system during engagement, increases the actual contact area during the soft-EHD lubrication system and reduces the actual contact pressure of the contact surfaces during the soft-EHD lubrication system.

DRAWINGS

1 FIG. 10 is a side view of a torque transmitting device incorporated between a drive shaft and an output shaft according to an exemplary embodiment of the present invention; FIG.

2 is a partially cut away view of the torque transmitting device of 1 according to an exemplary embodiment of the present invention;

3a is an enlarged partial cross-sectional view of the torque transmitting device of 1 with a plurality of elevations on a surface of an in 2 shown friction material layer according to the exemplary embodiment of the present invention are formed;

3b is an enlarged view of an in 3a survey shown; and

3c is an enlarged cross-sectional view of the torque transmitting device of 1 with the in 3a shown plurality of surveys and in a state of engagement according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numerals refer to like components, in FIG 1 a side view of a torque transmitting device 10 according to an exemplary embodiment of the invention. The torque transmitting device 10 is commonly referred to as a clutch or brake in automotive applications. The torque transmitting device 10 has a first plate or friction plate 12 and a second plate or reaction plate 16 on. The friction plate 12 is from the reaction plate 16 through a layer of lubricating fluid 14 separated. The lubricating fluid 14 is between the friction plate 12 and the reaction plate 16 arranged, and is used to create a smear boundary between the plates 12 and 16 provide.

The torque transmitting device 10 is between a drive shaft 18 and an output shaft 20 involved. In particular, the friction plate 12 with the drive shaft 18 coupled, and the reaction plate 16 is with the output shaft 20 coupled. The drive shaft 18 is typically connected to a torque generating device, such as an internal combustion engine (not shown). The output shaft 20 may be connected to a planetary gear set (not shown) to transmit a drive torque from the engine to the planetary gear set to drive the wheels of a motor vehicle. However, each of the plates 12 . 16 the torque transmitting device 10 also be connected to a rotating element or with a non-rotating element. Both the friction plate 12 as well as the reaction plate 16 are made of steel or a similar material. However, those skilled in the art will recognize that the present invention can be applied to plates made of other materials, such as metal alloys, composites, or the like.

Now up 2 Referring to Fig. 12, a partially cut away view of the torque transmitting device will be shown 10 from 1 according to the exemplary embodiment of the present invention. Parts of the reaction plate 16 were removed to the smear layer 14 and a friction material layer 22 to disclose. The Friction material layer 22 is on a surface 23 the friction plate 12 appropriate. The friction material layer 22 may include any of a variety of friction materials commonly used today in torque transmitting mechanisms. However, the present invention contemplates that the friction material layer 22 of cellulose, kevlar and resin or any combination of these materials in varying percentages by weight that may or may not be used in current coupling applications. The friction material layer 22 is a compressible yielding material that returns to its initial height and shape before leaving the reaction plate 16 is compressed, provided that the friction material layer 22 is not compressed beyond its elastic limit.

In the preferred embodiment of the present invention, the friction material layer 22 a plurality of elevations or indentations 26 on that on a surface 24 the friction material layer 22 are formed. The surveys 26 are over the surface 24 the friction material layer 22 arranged in a predefined pattern and evenly spaced. As shown, the surveys are 26 radially aligned. It should be emphasized that the surveys 26 may be arranged in a variety of patterns, including a random pattern. The density of the surveys 26 over the surface 24 can also be varied depending on the particular application or the desired performance criteria.

Now up 3a and 3b Referring to Figure 12, a partial cross-sectional view of the torque transmitting device will be described 10 through a plurality of surveys 26 in 3a shown. Furthermore, an enlarged view of a survey 26 in 3b shown. Every survey 26 has a substantially circular edge 28 on. The edge 28 has a predefined height relative to the surface 24 the friction material layer 22 , Every survey 26 also has one of the edge 28 defined cavity 30 on. Every cavity 30 has a substantially round bottom surface. However, it should be emphasized that the bottom surface of the cavity 30 can be formed with a different shape. Every survey 26 is shaped such that the cavity 30 is deep enough to lubricate the fluid 14 during the clutch operation taking into account the elastoplastic deformation and wear of the friction material layer 22 withhold. However, the predefined depth of each cavity allows 30 that the lubricating fluid 14 over the edge 28 running. During engagement of the clutch 10 becomes the lubricating fluid 14 from the cavity 30 pressed or forced and flows over the edge 28 on the surface 24 the friction material layer 22 to get between the layer 22 and the plate 16 to produce a thin film of the lubricating fluid. Every edge 28 serves to the thin film of the lubricating fluid 14 to penetrate what the contact area between the friction material layer 22 and the reaction plate 16 elevated.

As in 3a shown is the torque transmitting device 10 in a non-engaged state. During the non-engaged state, the reaction plate touches 16 the friction material layer 22 not, and therefore no load is transmitted. As shown, the friction material layer is 22 not compressed. During the non-engaged state, the friction material layer is facing 22 a thickness T _uc on. In particular, when force on the torque transmitting device 10 is applied, the surveys 26 and the friction material layer 22 pressed together. The edge 28 of each survey 26 has a predefined height relative to the surface of the friction material layer 22 , The height of each edge 28 prevents the friction material layer 22 is compressed beyond a predefined elastic zone.

Now up 3c Referring to Fig. 12, a partial cross-sectional view of the torque transmitting device will be described 10 from 3a according to the exemplary embodiment of the present invention. As shown, the torque transmitting device is located 10 in an engaged state. During the engaged state, the reaction plate 16 and the friction plate 12 moving in the direction of each other. In particular, the reaction plate touches 16 the surveys 26 and pushes the friction material layer 22 together. As a result of compression, the lubricating fluid 14 from the cavity 30 forced. In addition, every edge penetrates 28 of each survey 26 the lubricating fluid 14 that is from the cavity 30 is forced, which causes the load evenly over the entire surface 24 the friction material layer 22 is distributed.

In summary, the present invention has many advantages and benefits over the prior art. The teachings of the present invention can be used to overcome the many problems encountered with torque transmitting devices 10 can be found by the prior art. For example, the surveys break through 26 the film during the initial engaged state, which is the area of contact between the reaction plate 16 and the friction material layer 22 increases and the contact pressure between the reaction plate 16 and the friction plate 12 decreases. The surveys 26 also distribute the load evenly over the entire section of the surface 24 the friction material layer 22 , The surveys 26 also extend the soft-EHD state by removing the lubricating fluid 14 in the cavities 30 withheld and the necessary amount through the friction material layer 22 to distribute. In addition, the surveys prevent 26 in that the friction material layer 22 overheated, as the lubricating fluid 14 in the cavities 30 collected and evenly over the friction material layer 22 during compression of the friction material layer 22 is dispersed on an as-needed basis. The surveys 26 minimize the amount of fluid that is necessary to allow the torque transmitting device 10 works optimally what the required oil pump performance during operation of the torque transmitting device 10 decreases. The surveys 26 also extend the slip time without shudder and increase the power density of the torque transmitting device 10 without Shudder.

Claims (12)

Clutch ( 10 ) comprising: a reaction plate ( 16 ) configured to apply a compressive force; a friction plate ( 12 ) having a surface opposite the reaction plate; a friction material layer ( 22 ), which is a first, on the surface of the friction plate ( 12 ) and a second, the reaction plate ( 16 ) opposite surface ( 24 ), wherein on the second surface ( 24 ) a plurality of surveys ( 26 ) predefined height relative to the surface ( 24 ) of the friction material layer ( 22 ), each one of an edge ( 28 ) surrounded cavity ( 30 ) have a predefined depth; and one between the reaction plate ( 16 ) and the friction material layer ( 22 ) arranged lubricating fluid ( 14 ) to transfer the compressive force and between the reaction plate ( 16 ) and the friction plate ( 12 ) a smear layer ( 14 ) to provide; characterized in that the predefined depth of the cavity ( 30 ) is less than the predefined height of the surveys ( 26 ), so that in the cavity ( 30 ) located lubricating fluid ( 14 ) during engagement of the clutch ( 10 ) from the cavity ( 3 ) is pressed or pressed and over the edge ( 28 ) on the surface ( 24 ) flows. Coupling according to claim 1, in which the friction material layer ( 22 ) is a compressible compliant material that is at a predefined height of the friction material layer ( 22 ) before it is removed from the reaction plate ( 16 ) is compressed. Coupling according to Claim 2, in which the friction material layer ( 22 ) is plan. A coupling according to claim 1, wherein each of said plurality of projections ( 26 ) is a compressible compliant material which returns to the predefined height before being removed from the reaction plate ( 16 ) is compressed. Coupling according to claim 4, wherein the cavity ( 30 ) is shaped to the lubricating fluid ( 14 ) to keep. A coupling according to claim 4, wherein the rim ( 28 ) has a circular shape. Coupling according to Claim 5, in which the cavity ( 30 ) has a round bottom surface. A coupling according to claim 1, wherein each of said plurality of projections ( 26 ) on the second surface ( 24 ) of the friction material layer ( 22 ) is evenly spaced. A coupling according to claim 1, wherein the plurality of protuberances ( 26 ) on the second surface ( 24 ) of the friction material layer ( 22 ) (i) is arranged in a predefined pattern and / or (ii) in a random pattern. A coupling according to claim 9, wherein the plurality of elevations ( 26 ) is arranged in the predefined pattern. A coupling according to claim 10, wherein the plurality of projections ( 26 ) is radially aligned. A coupling according to claim 9, wherein the plurality of elevations ( 26 ) is arranged in the random pattern.

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